Low-temperature Co-fired Ceramic Structure Research Articles

LTCC Strip Electrode Arrays for Gas Electron Multiplier Detectors.

The Low Temperature Cofired Ceramic (LTCC) technology has proven to be highly suitable for 3D microstructures manufacturing in electronic devices due to its excellent electrical and mechanical properties. In this paper, a novel idea of implementing the LTCC structures into high-energy particle detectors technology is proposed. It can be applied in High Energy Physics (HEP) laboratories, where such sophisticated sensors are constantly exposed to particles of the TeV energy range for many years. The most advanced applications of the concept are based on dedicated gas amplifier systems coupled with readout microstructures. Typically, the readout microstructures are made in the Printed Circuit Boards (PCB) technology and processed in a sophisticated and patent-protected way. This article presents the manufacturing process and parameters of the novel microstructures made in the LTCC technology. The structures were implemented into the high-energy particle detector, and the first results are presented.

The origin of interfacial delamination in Au/ceramic cofired LTCC structure

The interfacial delamination of electrode/ceramic multilayer structure will seriously damage the reliability of low temperature co-fired ceramic (LTCC) module in practical applications. In this work, three kinds of glasses employed in Au electrode are designed and prepared to study the abnormal expansion and delamination process in the Au/ceramic LTCC multilayer structure. The interfacial delamination in the co-fired structure is found to be attributed to the abnormal expansion of glass in respect to Au electrode at high temperature, which is originated from the enlarged closed pores during the co-firing process. This conclusion is further confirmed by co-firing the sample in a low-pressure condition. The mechanism and elimination of interfacial delamination here provides a feasible solution for the design of novel glasses in Au electrode for LTCC applications.

The investigation of basic microfluidic elements in LTCC structures

PurposeThe purpose of this study is to design, fabricate and investigate low-temperature co-fired ceramic (LTCC) structures with integrated microfluidic elements. Special attention is paid to the study of fluid properties of micro-channels and microvalves, which are important constitutive parts of both, microfluidic systems and individual microfluidic devices.Design/methodology/approachSeveral test patterns of fluid channels with different geometry and different types of valves were designed and realized in LTCC technology. All test structures were tested under the flow of two fluids (liquids): water and isopropyl alcohol. Flow rates at different applied pressure were measured and hydrodynamic resistance and diode effect were calculated.FindingsThe investigation of the channels showed that viscosity of fluidic media has significant influence on the hydrodynamic resistance in channels with rectangular cross-section, while this effect is small on channels with square cross-section. The viscosity also has a decisive influence on the diode effect of different shape of valves, and therefore, it is important in the selection of the valve in practical applications.Research limitations/implicationsIn this work, the investigation of hydrodynamic resistance of channels and diode effect of passive valves is limited on selected geometry and only on two fluidic media and two applied pressures. All these and some other parameters have a significant influence on fluidic properties, but this will be the topic of the next research work, which will be supported by numerical modelling.Practical implicationsThe presented results are useful in the future designing process of LTCC-based microfluidic devices and systems.Originality/valueMicrofluidic in the LTCC structures is an unconventional use of this technology. Therefore, the fluid properties are relatively unsearched. On the other hand, the global use of microfluidic devices and systems is growing rapidly in various applications. They are mostly made by polymer materials, however, in more demanding applications; ceramic is a useful alternative.

LTCC Filtering Rat-Race Coupler Based on Eight-Line Spatially-Symmetrical Coupled Structure

In this paper, a compact filtering rat-race coupler implemented in low-temperature co-fired ceramic (LTCC) technology is presented. In order to reduce the dimensions, the schematic and the coupling topology of a planar filtering rat-race coupler are first studied and then simplified to fit the 3-D multilayer LTCC structure. An eight-line spatially symmetrical coupled structure is, therefore, proposed to obtain the required coupling topology between resonators. Thus, the filtering rat-race coupler can be constructed only by using four resonators, which is only half that of the planar one. Consequently, the size could be reduced substantially. For validation, a design example centered at 3.5 GHz is simulated, fabricated, and measured. All the measured results are in good agreement with the full-wave simulation results. Besides, the size of the circuit is only $3.8 \times 4 \times 2.1$ mm3, which demonstrates that by employing the eight-line spatiallysymmetrical coupled structure, the proposed rat-race coupler obtains good performance and compact size.

Compact High-Isolation LTCC Diplexer Using Common Stub-Loaded Resonator With Controllable Frequencies and Bandwidths

In this paper, a low-temperature co-fired ceramic (LTCC) diplexer is presented with compact size and high isolation. By using the common stub-loaded resonator shared by two channel filters, combining and matching networks are eliminated and only three resonators are used to design the two second-order channel filters, resulting in simple structure and miniaturized size. A novel transmission path is utilized to not only realize the higher channel filter but also prevent the signal at the lower frequency band. And a specific coupling region is selected to simultaneously realize the coupling strength required by lower channel filter and a transmission zero at higher-band frequency. In this way, each channel filter can generate a transmission zero at the passband frequency of the other channel filter, resulting in high isolation. Moreover, the bandwidths and center frequencies of the two channel filters can be individually controlled due to the design flexibility of the multilayer LTCC structure. For demonstration, a diplexer operating at 3.5 and 5.5 GHz is fabricated. The core circuit has the compact size of 1.9 mm $\times1.7$ mm $\times2$ mm or $0.054~\lambda _{g} \times 0.048 \lambda _{g} \times 0.057~\lambda _{g}$ . Within the 3-dB passbands of the lower and higher channel filters, the measured isolation levels are better than 40 and 45 dB, respectively.

Multilayer LTCC structures based on glass-cordierite layers with different porosity

PurposeThe paper aims to report on fabrication procedure and present microstructure and dielectric behavior of multilayer porous low-temperature cofired ceramic (LTCC) structures based on glass-cordierite and glass-alumina.Design/methodology/approachThe LTCC structures were created as multi-layered composites with dense external layers and inner layers with intentionally introduced porosity. Two preparation methods were applied – subsequent casting of both kinds of slurries and conventional isostatic lamination of dried green tapes arranged in the designed order. Optical microscope observations were carried out to analyze the microstructure of green and fired multilayer structures and pore concentration. To evaluate the adhesion strength of the composite layers, pull test was performed. Dielectric behavior of the composites was studied in the frequency range 50 kHz-2 MHz.FindingsThe fabricated porous LTCC structures showed dielectric constant of 3-5.6. The lowest dielectric constant was attained for glass-cordierite composite made by the conventional tape casting/lamination/firing method from slurry with 50 per cent graphite content. The samples prepared using multiple casting were of worse quality than those fabricated in conventional process, contained irregular porosity, showed tendency for deformation and delamination and exhibited a higher dielectric constant.Originality/valueSearch for new low dielectric constant materials applicable in LTCC technology and new methods of their fabrication is an important task for development of modern microwave circuits.

Design and integration of a piezoelectric vibrating device in an LTCC structure

PurposeIn this contribution, the design and integration of a piezoelectric vibrating device into low-temperature, co-fired ceramic (LTCC) structures are presented and discussed. The mechanical vibration of the diaphragm was stimulated with a piezoelectric actuator, which was integrated onto the diaphragm. Three different methods for the integration were designed, fabricated and evaluated.Design/methodology/approachThe vibrating devices were designed as an edge-clamped diaphragm with an integrated piezoelectric actuator at its centre, whose role is to stimulate the vibration of the diaphragm via the converse piezoelectric effect. The design and feasibility study of the vibrating devices was supported by analytical methods and finite-element analyses.FindingsThe benchmarking of the ceramic vibrating devices showed that the thick-film piezoelectric actuator responds weakly in comparison with both the bulk actuators. On the other hand, the thick-film actuator has the lowest dissipation factor and it generates the largest displacement of the diaphragm with the lowest driving voltage. The resonance frequency of the vibrating device with the thick-film actuator is the most sensitive for an applied load (i.e. mass or pressure).Research limitations/implicationsResearch activity includes the design and the fabrication of a piezoelectric vibrating device in the LTCC structure. The research work on the piezoelectric properties of integrated piezoelectric actuators was limited.Practical implicationsPiezoelectric vibrating devices were used as pressure sensors.Originality/valuePiezoelectric vibrating devices could be used not only for pressure sensors but also for other type of sensors and detectors and for microbalances.

LTCC Based Planar Inductive Proximity Sensor Design

This paper is focused on design and realization of planar inductive sensor system used for proximity sensing based on Low Temperature Co-fired Ceramics (LTCC). Planar coil consisting of six layers was designed, produced and measured. Electronic system for driving coil and processing measured values was developed and realized. Proximity measurement of various metal materials was realized and results were processed and evaluated. Measurements has shown that six‑layers LTCC structure with implemented coils in cooperation with developed driving electronic is appropriate solution for design and construction of planar proximity sensor. It had been developed sensitive inductive sensor for up to 7 millimeters distance proximity measurements.

Reduction of dielectric constant of LTCC substrates by introduction of controlled porosity

Purpose This paper aims to present a method for the reduction of dielectric constant of low-temperature co-fired ceramics (LTCC) substrates with the use of controlled internal porosity. Design/methodology/approach A glass-ceramic green tape with addition of graphite as a pore former was developed. The green tapes were laminated and then sintered into multilayer structures with porous interior and thin external dense layers. Microstructure of green and fired structures was studied using optical and scanning microscopy. The behavior of the samples during heating was examined in a heating microscope. Impedance spectroscopy was applied for investigation of dielectric properties of the fabricated substrates. Findings Microstructure and dielectric properties of the fabricated LTCC structures were compared with the characteristics for non-porous samples with the similar composition. Introduction of 50 Wt.% admixture of graphite in the internal layers of the LTCC substrate was found to result in decrease in dielectric constant value down to about 3. Application of non-porous outer layers improved mechanical strength of the structure and smoothness of its surface, allowing screen printing of conductive pastes on both sides of the substrate. Practical implications The rapid growth of the wireless communication industry has created a great demand for the development of new and improved materials and devices operating properly at high frequencies. The fabricated materials can be useful for substrates of microwave devices. Originality/value The paper presents an innovative method of dielectric constant decrease of substrate materials. Getting insight into the phenomena responsible for formation of pores is crucial for designing materials for microwave electronics.

Synthesis and Implementation of LTCC Bandpass Filter With Harmonic Suppression

In this paper, we utilize the coupling matrices to design a compact low-temperature cofired ceramic (LTCC) bandpass filter with wide stopband and high selectivity. One coupling matrix at the fundamental frequency is synthesized to obtain required passband responses. The other one at the third harmonic is manipulated to realize wide stopband. Two transmission zeros are appointed at both sides of the passband to enhance the skirt selectivity. They are generated by multiple cross-coupling paths, which are easy to realize in the multilayer LTCC structure. To reduce the circuit size, two coupled quarter-wavelength resonators are folded vertically and horizontally on different layers. An experimental filter is designed for verification. High skirt selectivity and wide stopband are observed in the measurement. Due to the LTCC techniques, the proposed circuit has a compact size of $2~\text {mm}\times 1.7~\text {mm}\times 2$ mm or $0.042\lambda _{g}\times 0.035\lambda _{g}\times 0.042\lambda _{g}$ . It is suitable for system-in-package applications.

Influence of B2O3–SiO2–ZnO–BaO glass ratio and sintering temperature on the microstructure and property of copper thick film for low temperature co-fired ceramic

In this study, B2O3–SiO2–ZnO–BaO (BSZB) glass-coated copper particles were prepared by sol–gel process for use in copper pastes. The pastes with different ratio of BSZB glass were sintered at temperatures ranging from 850 to 910 °C with low temperature co-fired ceramic (LTCC) substrate. When pastes prepared from 1 wt% glass-coated copper powder were sintered at 910 °C, both a dense copper film and a dense LTCC structure were obtained. At this condition, the film had a thickness of approximately 15 μm and a sheet resistance of 1.9 mΩ/□, and a good bonding behavior between copper film and LTCC substrate was also observed.

Triband Filter Design Using Laminated Waveguide Cavity in LTCC

This paper demonstrates the flexibility and superiority of multilayer low-temperature cofired ceramic structures in realizing filters with multifunction features. A systematic synthesis technique is employed to develop triband laminated waveguide filters with minimum number of resonators and improved band allocation. By exploiting the multiple resonant modes inside a cavity, the coupling mechanisms and feeding design for different bands can be selectively controlled in accordance with the modal field distributions. Thus, the different passbands can be treated with different methodologies to achieve the multiband function with flexible band allocation. A triband filter operated at 30, 35, and 37 GHz with a fourth-order quasi-elliptic response for the first band and a split-type response for the last two bands is developed. It shows only four cavities are needed with the overall circuit size of 4.9 × 4.1 × 0.88 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Experimental and simulated results are in good agreement, both validate the design concept.

Improvement in the Low-Fire Dielectric Compositions with Middle Permittivity for LTCC Applications

Low temperature co-fired ceramics (LTCC) technology becomes crucial in the development of various modules and substrates in electronic packaging, especially in wireless and microwave applications [. self-integrated component has laid basis on flexibility of design, wiring density and dependability for multilayer structures due to LTCC technology. Recently, with the rapid progress in wireless communications,to realize more highly integrated passive components in multilayer LTCC structure, however, it is important to control the matching behavior between component and substrate. The dielectric compositions the permittivity range of which is 20100 are most appropriate for realizing strip or microstrip resonator structures in LTCC multilayer structures due to the RF frequency range which is used in current telecommunication systems (130GHz) and the desirable chip sizes in the current technologies (210 mm)[.

Comparison of LTCC inductors on different substrate configurations with PCB inductor

Purpose – This paper presents performance comparison of RF inductors with the same lateral geometry applying different substrate configurations. The purpose of presented research is to demonstrate and verify some advantages of low temperature co-fired ceramic (LTCC) technology in comparison to printed circuit board (PCB) technology based on the performance analysis of presented inductors in lower RF range. Design/methodology/approach – The presented inductors are meander structures fabricated in LTCC and PCB technology, with same line width and outer dimensions. Performance analysis of all configurations is based on measurement results and numerical simulations. Advantage of LTCC technology is demonstrated by application of substrate pattering in order to maintain and/or improve expected inductor performances. Findings – As expected, obtained results for the inductor with an air-gap show increase of the quality factor over 30 percent and widening of the operating frequency range by 50 percent when compared with the same LTCC structure without a gap. But what is more important the inductor with air-gap embedded inside LTCC stack maintains efficiency when compared to PCB inductor. This fact offers possibility of integration good quality components inside LTCC stack and reduction of used chip space. Originality/value – Advantages of LTCC with respect to PCB design are demonstrated by efficiency increase of the proposed inductor configurations by means of design optimization relying on substrate pattering and incensement of the packaging density by embedding inductors. The presented findings are verified through consistency of measurement results and simulated data.

Substrate integrated waveguide filter with embedded mixed source–load coupling

A compact substrate integrated waveguide (SIW) filter with an improved stopband using multilayer embedded mixed coupling (MC) is presented. By implementing MC into the input/output SIW, the filter not only exhibits good rejection for the upper stopband, owing to an additional controllable transmission zero, but also has a miniature size of 18 × 12 mm2 by profiting from its low-temperature co-fired ceramic structure. An experimental second-order filter with three TZs has been designed and fabricated. The measured results show good agreement with the simulated ones.

Surface modification of low and high temperature co-fired ceramics for enzymatic microreactor fabrication

In this work, immobilization of enzyme (urease) on substrates made of low temperature co-fired ceramics (LTCC) and high temperature co-fired ceramics (HTCC) is presented. The research was performed for three various LTCCs (DP951, CeramTec GC, HL2000) and one HTCC (ESL 44000) material system. Investigated ceramic materials were characterized using energy dispersive spectroscopy (EDS) and contact angle measurements. Immobilization method based on APTS (3-aminopropyltriethoxysilane) and glutaraldehyde is proposed for LTCC and HTCC surface modification. Effectiveness of the applied immobilization procedure was examined using Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) technique. Changes in surface composition of the LTCC and HTCC-based test structures are examined after each step of the immobilization process. On the basis of performed experiments one ceramic material system was chosen for fabrication of the enzymatic microreactor. Performance of the ceramic microreactor with immobilized urease was examined experimentally, as well.

Localized Temperature Stability in Low‐Temperature Cofired Ceramics

Low‐temperature cofired ceramic (LTCC) is a multilayer 3D packaging, interconnection, and integration technology. For LTCC modules targeting radio and microwave frequency (RF and MW) applications, a low or near 0 ppm/°C temperature coefficient of resonant frequency (τf) ensures temperature stability of embedded resonator and filter functions. The base dielectrics of most commercial LTCC systems have a τf in the range −50 to −80 ppm/°C. This study explored a method to achieve a zero τf on stripline (SL) resonators by locally cofiring, in a multilayer LTCC structure, compensating dielectrics (CD) with an opposite τf to that of the host dielectric. The formulation, synthesis, dielectric properties, and microstructure of SrTiO3 (STO)‐based low‐fire τf CD are presented. Chemical interactions and physical compatibility between the compensating and the host LTCC dielectrics are investigated for cofireability. The dependence of τf compensation on the wt% of STO, the printed thickness, and the location of the CD in multilayer LTCC are discussed. The most effective τf compensation is achieved by integrating CD next to the resonator lines, and can be explained by the concentration of electromagnetic energy via total internal reflection of electromagnetic waves inside the CD layer.

Thermal analysis of starch for realizing embedded channel in low temperature co-fired ceramic

The rapidly developing biotechnology, automotive industry, chemical and environmental fields have increasing needs for analytical systems with desires such as smaller sizes, lower sample volumes. Reduction in size results in further requirements in functionalities such as multi-sensor devices with low cost. These microsystems usually contain three-dimensional structures. In the fabrication of microfluidic devices ensuring a well-shaped channel is a challenge. During firing of the low temperature co-fired ceramic (LTCC) substrate, these embedded structures tend to deform and sag because the green glass–ceramic material is very weak. Starch was used as sacrificial volume material (SVM) to support the embedded structures of the LTCC during lamination and sintering. As a consequence of burnout, the increased fraction of evolving gases from SVM requires an adequate adaptation of the firing process to control starch degradation and provide a residue-free burnout. Using thermal analysis techniques and describing degradation kinetics of SVM, a new heating profile is demonstrated which insures complete starch burnout without damaging the LTCC structures.

Design of an LTCC Structure for a Micro-Ceramic Combustor

Advanced micro- or macro-systems are in some cases made with multilayer ceramic technology. Low-Temperature Co-fired Ceramic (LTCC) technology is considered as one of the more suitable technologies for the fabrication of ceramic micro-systems that integrate screen-printed, thick-film electronic components as well as three-dimensional buried structures, for example, cavities and channels. One of the applications is a ceramic combustor. The chemical energy of the fuel is converted into thermal energy in a chemical micro-combustor through a burning process, while the accompanying high temperatures and, frequently, high pressures impose harsh conditions on the combustor structure. Therefore, the combustor must be carefully designed not only from the functional, thermal and chemical points of view, but also with respect to the mechanical strength. The combustor device was prepared by laminating of Du Pont 951PX LTCC green tapes. The fabricated 3D LTCC structures with buried cavities and channels including two inlets (for fuel and air), the evaporator for the fuel, the mixing system of the channels (for mixing the evaporated fuel and air), the distribution channels and eight microburners were realized. The main parts are eight micro-burners realized as buried cavities. In the burners a platinum-based catalyst was deposited to assist the oxidation, i.e., the burning, of the methanol with the air. Thickfilm, platinum-based heaters and temperature sensors are incorporated within the structure. The device was tested with different flow rates of liquid methanol (1 ml/h to 5 ml/h) and air (7 l/h to 15 l/h). The obtained temperatures were between 250°C and 450°C.

Characterization of the Fabrication Process of Rolled LTCC Structures

This work focuses on the fabrication and assembly of cylindrical plasma containment tubes using DuPont's 951 Low Temperature Co-fired Ceramics (LTCC) for use in miniature electrostatic thrusters. The use of LTCC allows for robustness post-firing yet flexibility in the “green” un-fired state. Some of the main advantages of this flexibility include the ability to stack or roll the LTCC sheets into various shapes as well as incorporating embedded electrical interconnections using silver paste on the rolled layers. The tube is used to contain argon plasma, which is generated by a spiral Inductively Coupled Plasma antenna and is also fabricated in LTCC. The tube also interfaces with two electrically biased grids on the opposite end, which accelerate the plasma out of the tube. These interfaces are highly dependent on the dimensions and tolerances of the containment tube. The development of the fabrication process will be presented for the incorporation of the tubes onto the base as a single structure. This includes constructing the antenna base, shaping the “rolled” LTCC containment tube using a jig and isostatic press, and integrating the tube and antenna base during the firing. Following the fabrication, measurements will be taken to determine the tube circularity and the hermeticity of the seal at the interface between the tube and the antenna base. The results will be presented and characterized to evaluate the effectiveness of the structure as well as the documentation of the development of a rolled LTCC tube structure integrated with a planar LTCC antenna base.